Distribution and developmental characteristics of sugars and organic acids in fresh apricots

Distribution and developmental characteristics of sugars and organic acids in fresh apricots | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Distribution and developmental characteristics of sugars and organic acids in fresh apricots Chenjuan Jing, Duan Wang, Zhikun Liu, Xuefeng Chen, Xiaohong Wu This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6028777/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 4 You are reading this latest preprint version Abstract This study systematically analyzed the distribution characteristics and developmental patterns of sugars and organic acids in apricots, exploring the accumulation and metabolism of organic acids, thus providing important information for improving fruit quality. High-performance liquid chromatography was used to determine the sugar and organic-acid contents and distributions in mature apricot fruits from 332 common seedlings and 64 germplasm resources. The results showed that glucose and sucrose are the main sugars in apricots, and the fruits were classified as sucrose-type, or two-sugar-type based on the calculated value of log 2 (glucose/sucrose). Malic and citric acids are the main organic acids in apricots, and the fruits were classified as malic-acid-type, citric-acid-type, or two-acid-type based on the value of log 2 (malic acid/citric acid). Analysis of the developmental patterns of sugars and organic acids in selected fruits revealed high glucose contents during their developmental stages. Fructose and sucrose contents were low, but increased during the ripening stage, particularly those of sucrose. Malic acid was the main organic acid during the development stage, accounting for over 90% of the total-organic-acid content. As the fruit matured, the malic-acid content decreased, while that of citric acid increased. Correlation analysis revealed a significant positive correlation between fructose and citric-acid contents, both of which increased during fruit ripening. Therefore, changes in citric-acid levels may be related to ripening. Overall, this result offers valuable foundation for improving flavor quality of apricot fruit. Apricot fruit Sugars Malic-acid-type and citric-acid-type Distribution characteristics Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Introduction Apricot ( Prunus armeniaca L.) is highly popular with consumers for its early ripening, excellent flavor, and nutritional value, making it one of the most important fruit crops in China (Liu et al. 2010 ; Wang et al. 2011 ). In 2016, the total apricot-cultivation area for the fresh market and processing in China exceeded 360,000 hectares, with a total yield of 2,700,000 tons (Haoyuan et al. 2019). Driven by consumer demand, higher-quality apricots have a greater commodity value. Specifically, sweet apricot varieties with low acidity are more favored by consumers and thus have greater market value. Conversely, sour-tasting apricots have limited economic value. The taste of a fruit is primarily influenced by the types and contents of sugars and organic acids therein. Sucrose and malic acid are the main sugar and organic acid, respectively, in apples, accounting for over 90% of the total sugar and total acid contents (Jing et al. 2020 ). In citrus fruits, the sugar contents range from 60 to 130 mg/g fresh weight (FW), with that of sucrose typically accounting for ~ 50% of the total. The organic-acid contents in citrus fruits fall in the range 6–11 mg/g FW, with malic and citric acid being most abundant (Mei et al. 2021 ). In peaches, which are important drupe fruits, the sugar contents range from 55 to 160 mg/g FW, with fructose and glucose being dominant in the young fruit and sucrose becoming dominant upon maturity. The organic-acid contents in peaches fall in the range 4–28 mg/g FW, with malic and citric acids being the main components at maturity, the specific contents of which vary depending on cultivar (Yanping et al. 2007). Plums, another highly cultivated variety of drupe fruits, are mainly Chinese species. Sucrose is the main sugar in plums with a content range of 24.8–152 mg/g FW, accounting for over 80% of the total sugars. Malic acid is the main organic acid in plums, with a content range of 11.8–66.38 mg/g FW (Shuo et al. 2016 ). Apricots are also drupe fruits, and their sugar contents range from 31 to 130 mg/g FW. The main sugars in apricots are glucose, sucrose, fructose, and sorbitol, among which sucrose is the dominant component, accounting for over 60% of the total sugar, followed by glucose, while fructose and sorbitol contents are relatively low, accounting for less than 30% of the total. Therefore, apricot fruits are classified as sucrose-type fruits (Ayse et al. 2010; Fan et al. 2017 ). The organic-acid contents of apricot fruits range from 9.5 to 54 mg/g FW, mainly comprising quininic, malic, and citric acids. Of these, quininic acid has the lowest content, accounting for just 2–12% of the total organic acid, while the combined contents of malic and citric acids account for over 90% of the total organic acids. Currently, the organic acids in apricots classify them as malic-acid-type fruits (Etienne et al. 2013 ; Zhang et al. 2010 ). However, existing research on sugars and acids in apricot fruits may be subject to inaccuracy due to the limited number of varieties typically studied. Furthermore, there are currently no reported studies on the changes in sugar and organic-acid contents during apricot fruit development(Baccichet et al. 2023 ). Accordingly, this study employed high-performance liquid chromatography (HPLC) to conduct a detailed analysis of the sugar and organic-acid contents and distribution ratios in mature apricot fruits from a natural population of 332 common apricot seedlings and 64 germplasm resources (local varieties or introduced varieties). Through classification and screening, we selected eight apricot varieties with outstanding characteristics, including sucrose-type and reducing-sugar-type specimens as well as malic-acid-type, citric-acid-type, and two-acid-type fruits. Detailed analysis of these specimens revealed the changes in their sugar and organic-acid contents during development. In doing so, this study provides data support for improving fruit quality, as well as elucidating the mechanisms by which sugars and organic acids are accumulated and metabolized. Overall, this work provides a scientific basis for the breeding of high-quality apricot varieties with high sugar and/or low acid contents. Materials and methods Natural seedling population This population consisted of 332 seedling materials, which were planted in 2009 at the Shijiazhuang Fruit Research Institute (SFRI-HAAFS; Shijiazhuang, Hebei Province, China, 38° 7' N, 114° 32' E). The trees were planted in north-south rows with a density of 1 m × 2 m and received routine management for irrigation and pest control. Samples were collected in May–June 2022, i.e., during fruit ripening. Since each tree represented a unique material, 15 fruits were randomly picked from the outer perimeter of each tree. These fruits were divided into three replicates, with five fruits per replicate. The samples were frozen for storage prior to analysis. Germplasm resources The apricot germplasm resources were introduced to the germplasm repository at the Shijiazhuang Fruit Research Institute at different times. The rootstock used was Armeniaca sibirica , and the planting density was 3 m × 4 m, with trees planted in north-south rows. Based on previous investigations of growth habits and fruit taste in combination with comprehensive evaluations of fruit appearance and flavor, 64 outstanding apricot germplasm resources were selected (Supplementary Table 1). Samples were collected during fruit ripening for the determination of sugar and organic-acid type and content. Additionally, six varieties, ‘Qingmisha’, ‘Hamazui’, ‘Zhenzhuyou’, ‘Jinhui’, ‘Shunpingganzhi’, and ‘Meishuo’, were selected from the resources as experimental materials. Samples were collected every week from 20 days after flowering until fruit ripening. Fifteen apricot fruits were randomly picked from the outer perimeter of each tree, then divided into three replicates with five fruits per replicate. Determination of sugars and organic acids The identification and characterization of sugars and organic acids (sucrose, glucose, fructose, sorbitol, malic acid, citric acid, and quininic acid) were conducted using HPLC techniques as previously described (Jing et al. 2016 ). Analysis of sugars was performed using a system comprising a Waters 2695 pump, a Multospher® Sugar 5u column (250 mm × 4.6 mm × 5 µm; Waters, USA), and a 2414 refractive index (RI) detector. The organic acids were determined using a system that comprised a RIGOL L-3000 pump, an HP-C18-AQ column (250 mm × 4.6 mm, 5 µm), and a photodiode array detector. The mobile phase consisted of 0.1 M phosphoric acid buffer (pH 3.1) with a flow rate of 1.0 mL/min at 30°C, and detection was carried out at 210 nm (Jing et al. 2020 ). Statistical data analysis Data processing and graph plotting were performed using Microsoft Excel 2007. Correlation analysis was conducted with IBM SPSS Statistics 19 (SPSS Inc., Armonk, NY, USA), and least-significant-difference analysis was used to establish the significance of differences between samples. Histograms and box plots were created using Minitab 16. Clustered heatmaps were generated using HemI 1.0. Hierarchical clustering and heat-map analysis of apricot cultivars and parameters were performed using squared Euclidean distance and average linkage clustering algorithms (Deng et al. 2014 ). Results Distribution characteristics of sugars and organic acids in fruits from natural apricot populations In the apricot fruits, the distributions of fructose and sucrose contents are close to normal population. Although the contents of these sugars are mainly controlled by multiple minor-effect genes and show quantitative traits, there are some major gene effects at play. In contrast, the distribution of fructose content is more inclined to show quality traits, with control by multiple minor-effect genes playing an auxiliary role. The mean fructose content is 12.34 mg/g FW with a low variance value of 25.22 mg/g FW. The fructose contents range from 3.71 to 43.79 mg/g FW, being mainly distributed in the range 7–15 mg/g FW (71.3% of the population). Glucose content of the nature apricot fruits population averaged 13.55 mg/g FW with a minimum of 3.02 mg/g FW up to a maximum of 51.37 mg/g FW. The glucose contents are mainly distributed at 5–13 mg/g FW, accounting for 59.82% of the total sugar. Sucrose, as the main sugar component in apricot fruit, average 33.28 mg/g FW and show the most variance (228.151 mg/g FW). The sucrose contents range between 0.009 and 88.84 mg/g FW, with 64.95% of the population distributed in the 22.5–47.5 mg/g FW range. The total-sugar content of apricot fruit is the sum of the contents of fructose, glucose, and sucrose, and its distribution is close to normal. The total sugar contents fall in the range 16.97–126.36 mg/g FW, with a mean content of 58.65 mg/g FW. The total sugar contents are mainly distributed at 27.5–82.5 mg/g FW, accounting for 87.92% of the total (Supplementary Table 2). Apricot fruits contain much less quininic acid than malic and citric acids. The three organic-acid contents distribution tend to be normal, but they also show the characteristics of data discontinuity. Therefore, the contents of these three organic acids are quantitative traits controlled by micro-polygenes, and they are also regulated by certain main genes, showing the characteristics of quality traits. Among them, quininic acid is the least abundant organic acid in apricot fruit. At its lowest content, it is difficult to detect, while the highest content is 5.61 mg/g FW. In the natural apricot group, the average quinine-acid content is 1.05 mg/g FW, and it is mainly concentrated in the range 0.625–1.625 mg/g FW, accounting for 67.69%. The malic-acid contents for this population average 9.13 mg/g FW with a distribution range of 1.6–22.4 mg/g FW, where the content is mainly concentrated in the 2.5–13.5 mg/g FW range (80.97% of the total population). For citric acid, the mean content in this population is 8.09 mg/g FW (Supplementary Table 2), and the content distribution ranges from 0.48 to 21.0 mg/g FW. The main concentrated distribution area is 1.5–12.5 mg/g FW, which accounts for 72.51% of the population. The total-acid content is the sum of the three organic acids above, and although their distributions tend to be normal, the continuity of the data is relatively poor. This suggests that the regulation of total-acid content involves both major genes and multiple minor-effect genes. The total organic-acid contents in the apricot fruit of this population are 8.54–28.57 mg/g FW and the mean value is 18.25 mg/g FW. The contents are mainly concentrated in the 12.5–21.5 mg/g FW interval, accounting for 79.15%. Distribution of sugars and organic acids in the fruits of apricot germplasm resources Table 1 Classes and contents of sugars and organic acids in apricot resource fruits N mean values (mg/g FW) standard deviation coefficient of variation minimum maximum skewness Fructose 64 12.71 6.28 49.40 2.94 29.70 0.30 Glucose 64 29.20 15.59 53.39 3.59 70.43 0.70 Sucrose 64 41.19 13.95 33.87 10.72 73.73 0.43 Total sugar 64 82.70 22.60 27.33 38.48 138.78 0.30 Quininic acid 64 0.83 0.63 76.13 0.25 4.83 4.28 Malic acid 64 6.14 3.05 49.60 1.60 13.60 0.49 Citric acid 64 5.62 4.99 88.66 0.10 16.84 0.64 Total acid 64 12.60 3.87 30.72 4.091 20.93 0.24 Sixty-four apricot resources, each with 15 mature fruits, are randomly divided into 3 groups. This leads to a total of 192 replicates for all the resources. In these independent replicates, significant differences among treatments on each sampling date are identified using Tukey's test with a significance level of P < 0.05. And two-years measurements for 64 resources were averaged. The fructose contents of the resource fruit fall in the range 2.94–29.70 mg/g FW. Compared with the natural group, the fructose content is slightly lower, but it is still within the same range. The mean fructose content for the resource fruit is 12.71 ± 0.80 mg/g FW, which is comparable to the natural population average. In terms of organic-acid content, the quininic-acid content range for the fruits of the apricot resource group is 0.25–4.83 mg/g FW, which coincides with the content range for the natural population. However, the average quininic-acid content in this population is 0.83 ± 0.08 mg/g FW, which is lower than that for the natural population. Similarly, the malic-acid contents for the apricot resource group are in the 1.60–13.60 mg/g FW range, which is within the content range of the natural group. However, the average value is 6.14 ± 0.38 mg/g FW, which is relatively low compared with the natural population. This population has a wide range of citric-acid contents at 0.1–16.84 mg/g FW, with its lowest and highest contents being beyond the corresponding range for the natural population. However, the average content is 5.62 ± 0.62 mg/g FW, which is lower than the average for the natural population. For total-acid contents, the distribution range for the apricot resource group is 4.09–20.93 mg/g FW, covering both the lowest and highest contents seen in this study. The average total-acid content is 12.6 ± 0.48 mg/g FW, which is lower than that for the natural population (Table 1). In the germplasm fruit, the absolute contents of fructose are the lowest (Fig. 3 A and 3 B), ranging from 2.17–35.48% and having relatively little influence on the total-sugar content. The distribution trend is not affected by the glucose and sucrose contents. The content distributions for glucose and sucrose show certain differences: the absolute content of glucose directly affects the total-sugar content of apricot fruit, and its relative content is distributed between 3.66% and 59.82%. In contrast, the absolute content of sucrose is relatively evenly distributed, with its relative contents ranging from 18.97–96.20%, making it the main sugar component for germplasm resources (Fig. 3 A and 3 B). Furthermore, some correlation may be found between the relative content of sucrose and the content of glucose. The germplasm fruits have the lowest quinine-acid contents and the smallest proportions, ranging from 1.60–24.58%. However, the distributions of malic and citric acids are different, with their relative contents ranging between 10.22–94.37% and 1.91–86.28%, respectively. Furthermore, in some apricot resources, the proportions of malic and citric acids are quite different. Whether from the perspective of absolute organic-acid content or relative content, there are some apricot resources with high proportions of malic acid and some with high proportions of citric acids. Therefore, we initially divided these resources into malic-acid-dominant type (mal-type) and citric-acid-dominant type (cit-type) (Fig. 3 C and 3 D). And there were similar distribution trends of sugars and organic acids in natural apricots group fruits (Supplementary Fig. 1 and Supplementary Fig. 2). Classification of fruit sugars and organic acids in apricot germplasm resources By analyzing the absolute and relative distribution characteristics of sugars and organic acids in apricot resource fruits, we clustered them by glucose and sucrose contents and malic and citric acid contents. The results show that, based on the main sugars contents, the resources can be clustered into four categories: Class I resources have mainly glucose contents with relatively high total-sugar contents; Class II resources have roughly equal glucose and sucrose contents along with high total-sugar contents; Class III resources have high sucrose contents; and Class IV resources have roughly equal glucose and sucrose contents but low total-sugar contents (Fig. 4 A). In terms of organic acids, the resources can be divided into two categories: Class I resources are high in citric acid, and their total-acid contents are generally high; the other category is mainly malic acid and contains many resources with low acid contents (Fig. 4 . B). We identified 53 apricot resources with a ratio of glucose and sucrose (G/S) in base 2 log transformation, i.e., ∣log 2 (G/S)∣, lower than 1.5. When G/S is between 0.3 and 3, the fruit glucose and sucrose contents are between 25% and 75%, so we classify such fruit as two-sugar-accumulating type (two-sugar type). Only ‘Mingxing No.1’ is classified as glucose-dominant type (glu-type), with its value of log 2 (G/S) being 1.66. There are 10 sucrose-dominant type (suc-type) resource varieties, especially ‘Qingmisha’ (G/S = 1:25.7), ‘Yuzhouhong’ (G/S = 1:25.3), ‘Qinxing’ (G/S = 1:16.5), and ‘Jingcuihong’ (G/S = 1:6.4). Their values of log 2 (G/S) are lower than − 2, meaning that the sucrose contents of these fruits are more than six-times their glucose contents, so they are classified as extreme sucrose resources (Fig. 5 A). Upon further analysis of the malic acid to citric acid (M/C) ratios in apricot fruits, we found that when ∣log 2 (M/C)∣ ≤ 1, the ratio of malic acid to citric acid is between 0.5 and 2, so they are classified as two-acid-accumulating type (two-acid type) resources. A total of 16 resources were classified as such, including ‘Meishuo’, ‘Shunpingganzhi’, ‘Shajinhong No1’, and 9-D1, whose values of log 2 (M/C) are all close to zero, indicating that the contents of malic acid and organic acid in the fruits of these varieties are equivalent (Supplementary Table 3). There are 27 resources for which log 2 (M/C) > 1, i.e., their M/C ratios are greater than 2, which we classify as a malic-acid-dominant type (mal-type) resource. Among these resources, there are 19 with log 2 (M/C) > 2, especially ‘Maohong’ (M/C = 32:1), ‘Jingcuihong’ (M/C = 36.8:1), ‘Jingxianghong’ (M/C = 38.2:1), ‘Hamazui’ (M/C = 39.7:1), ‘Lanzhoudajie’ (M/C = 47.8:1), and ‘Wanbai’ (M/C = 342.5:1), that have log 2 (M/C) values greater than 5. There are 21 resources with log 2 (M/C) values < 1, that is, their M/C ratios are less than 0.5, which we classify as a citric-acid-dominant type (cit-type). The fruits with log 2 (M/C) < − 2 include ‘Jinhui’ (M/C = 1:8.4), ‘Kate’ (M/C = 1:7.1), ‘Dailing’ (M/C = 1:6.1), ‘Jinshou’ (M/C = 1:6), ‘Zihe’ (M/C = 1:5.2), ‘Mingxing’ (M/C = 1:5), ‘Daguo’ (M/C = 1:4.7), ‘Sungold’ (M/C = 1:4.7) and ‘Zhenzhuyou’ (M/C = 1:4.4) (Fig. 5 B and Supplementary Table 3). 3.4 Correlation analysis of sugars and organic acids in apricot fruits There is a complex interconversion relationship between sugars and organic acids within the fruit. Not only can different kinds of sugars and organic acids transform with each other, their roles and contributions in the life activities of the fruit may also vary. The results of correlation analysis revealed that fructose had highly significant positive correlations with glucose, total sugar, citric acid, total acid, and glucose/sucrose ( r = 0.572, 0.510, 0.448, 0.453, 0.583; P < 0.01) and a significant negative correlation with sucrose ( r = − 0.270, P < 0.05). There is a very significant positive correlation between glucose and total sugar, glucose/sucrose, and sugar/acid ( r = 0.811, 0.800, 0.529; P < 0.01). Sucrose shows very significant positive correlations with total sugar and sugar/acid ( r = 0.476, 0.475; P < 0.01) and a very significant negative correlation with glucose/sucrose ( r = − 0.558, P < 0.01), and a significant negative correlation with total acid ( r = − 0.286, P < 0.05). Furthermore, total-sugar content shows very significant positive correlations with glucose/sucrose and glucose/acid ( r = 0.382, 0.630; P < 0.01). In terms of organic acids, citric acid shows significant negative correlations with quininic acid and malic acid/citric acid ( r = − 0.261, − 0.289; P < 0.05) and very significant negative correlations with malic acid and sugar/acid ratio ( r = − 0.598, − 0.457; P < 0.01). However, there is a very significant positive correlation between citric-acid content and total-acid content ( r = 0.795, P < 0.01). Total-acid content had highly significant negative correlations with malic acid/citric acid and sugar/acid ( r = − 0.352, − 0.728; P < 0.01), and a significant positive correlation was found between malic acid/citric acid and sugar/acid ( r = 0.290, P < 0.05) (Table 2). Table 2 Results of correlation analysis for sugars and acids Fructose Glucose Sucrose Total sugar Quininic acid Malic acid Citric acid Total acid Malic acid/ Citric acid Sugars/ acids Fructose 1.000 0.572 ** -0.270 * 0.510 ** -0.194 -0.126 0.448 ** 0.453 ** -0.172 -0.046 Glucose 1.000 -0.074 0.811 ** -0.021 -0.128 0.049 -0.038 -0.045 0.529 ** Sucrose 1.000 0.476 ** 0.025 -0.145 -0.138 -0.286 * -0.111 0.475 ** Total sugar 1.000 -0.072 -0.201 0.086 -0.055 -0.145 0.630 ** Quininic acid 1.000 0.009 -0.261 * -0.173 -0.025 0.077 Malic acid 1.000 − .598 ** -0.005 0.035 -0.193 Citric acid 1.000 0.795 ** -0.289 * -0.457 ** Total acid 1.000 -0.352 ** -0.728 ** Malic acid/ citric acid 1.000 0.290 * Sugars/acids 1.000 Note: Total of 64 apricot resources were considered and replicated measurements for each cultivars were averaged. Correlations were significant * at the 5% and ** 1%. Development trends for sugar and organic acids in apricot fruits Since no extreme glu-type germplasm was identified in the apricot fruit resources, we screened the two-sugar-type and suc-type resources, thoroughly exploring the variability in sugar levels during fruit development. During the developmental cycle of the fruits of apricot resources, the glucose contents change very little. Among them, the glucose contents in the two-sugar-type apricot fruits approximately double during the ripening stage, while the change in the suc-type fruit is not significant. Both fructose and sucrose contents are maintained at relatively low levels during the early development and expansion stages. However, the two sugar levels increase differently when the fruit reaches maturity, about 7–14 days before the fruit is fully ripe. Among them, in the two-sugar-type apricot varieties ‘Shunpingganzhi’ and ‘Hamazui’, the increases in fructose and sucrose contents are similar, both 6–9-fold. In contrast, the fructose contents of ‘Qingmisha’ and ‘Lanzhoudajie’ increase 2–4-fold during the ripening stage, but their sucrose content increases ~ 10-fold (Fig. 6 ). In the course of development, the quininic-acid contents change little, but then changes significantly with the maturity of the fruit. At the same time, malic acid, as the main organic acid in the apricot fruit, always maintains a high level during the fruit growth and development process. However, as the fruit enters the ripening stage (7–14 days before maturity), the malic-acid contents all show significant downward trends. The malic-acid content is decreased to 30–50% that of the developmental stage in the ripening stage and to 20% or even lower in the cit-type resources. Although the content of citric acid is low in the fruit growth and development stage, in middle and late fruit development, its content increases significantly in the cit-type and two-acid-type apricot fruits. Since a relatively high initial content of malic acid is observed, followed by a large decrease in the mature period, the total-organic-acid contents also show an overall decreasing trend (Fig. 7 ). Discussion The sugars in fruits mainly include fructose, glucose, and sucrose, so different varieties can be divided into reducing-sugar-type, suc-type, and two-sugar-type fruits based on their characteristics (Lijing et al. 2015 ). In this study, a systematic analysis of the sugar compositions of natural populations and fresh apricot fruits showed that the fructose content is lower compared with the other two sugars, and there are differences between varieties, which is consistent with previous reports (Baccichet et al. 2022 ). In cultivated apricot fruits, the glucose and sucrose contents and their ratios show remarkable diversity among different varieties. By setting∣log 2 (G/S)∣< 1.5 as a criterion, this study divides fruit into sucrose, glucose (reducing-sugar type), and two-sugar types. Among them, two-sugar resources account for more than 80%, sucrose resources account for about 15%, and the existence of extreme suc-type apricot varieties and glucose (reducing-sugar) resources is extremely rare. It is important to note that existing research focuses on different sugar contents in apricot fruit, and with the formula in this study, can also introduce similar sugar classification, for example, Caliskan et al. classified 15 apricot resource varieties into two sucrose, one glu-type (reducing sugar), and 12 two-sugar types (Supplementary Table 4) (Caliskan et al. 2012 ). In fact, this difference in sugar composition is very common in apricot fruits, and many studies have highlighted this point, but few studies have fully explored this phenomenon. From the perspective of fruit development, the proportional distribution of sugar has stage characteristics. In the ripening stage, the type of sugar changes, while in the young and expansion stages, reducing sugars such as fructose and glucose are dominant, acting as the main energy materials for the development of reduced sugar crops (Li et al. 2018 ). When the apricot fruit enters maturity, organic matter accumulates mainly as sucrose, leading to a change in the sugar type of the fruit. The results of our correlation analysis indicate that fructose, glucose, and sucrose are negatively correlated, that is, the reduced-sugar content decreases and is converted into sucrose, which gradually accumulates in the fruit. This trend is also seen in fruits such as apples, citrus, and peaches (Du et al. 2024 ; Jing et al. 2020 ; Kongjie et al. 2022; Yanping et al. 2007). Another key factor affecting the taste of apricot is the organic acid content, the average value of which is 12.60 ± 0.48 mg/g FW, making it a high-acid fruit and thus unappetizing to certain consumer groups. In this study, an extremely high proportion of citric acid varieties were present in apricot fruits. Therefore, we classified the fruit acid type according to the log 2 (M/C) criteria presented above. Previous studies have pointed out that the organic acids in apricot fruits can be classified as malic acid and citric acid, but only two varieties, New (malic acid) and Kate (citric acid), have been studied, providing results that are consistent with those of this study (Meixia et al. 2006). In addition, when the apricot varieties reported in the literature were classified, we found that the log 2 (M/C) values of ‘Dajiexing’, ‘Kaili’ and ‘Luotuohuang’ were 4.00, 7.45, and 6.60, respectively, belonging to the mal-type, which are consistent with the classification results in this study (Fan et al. 2017 ; Zhang et al. 2010 ). Similarly, log 2 (M/C) values of − 2.43 and − 2.06 have been reported for Kate, classifying it as cit-type, which is consistent with our study results (log 2 (M/C) = − 2.83) (Chen et al. 2006 ; Fan et al. 2017 ). In fact, French researchers have long been aware of the diversity in malic acid and citric acid contents in apricot germplasm resources, and revealed the genotype differences in the ratio of malic acid/citric acid through principal component analys is (Gurrieri et al. 2001 ). This finding coincides with the results of the present study. However, apricot fruits are not rich in organic acid species. This study classified apricot resources into mal-type, cit-type, and two-acid type, and found that malic acid accounted for more than 90% of the total acid in the fruit development stage, while the other acids were less abundant, accounting for less than 10%. This rule is consistent with the organic acid changes in developing fruits such as apple and jujube, which are dominated by malic acid (Jing et al. 2016 ; Zhang et al. 2023 ). The richness of apricot fruit acid types is mainly reflected in the fruit ripening period. Although the total-acid content decreases, which is mainly due to the lower malic-acid content, the citric-acid content increases in some varieties. The results of correlation analyses for natural apricot group and resource fruit also confirmed that citric-acid content is negatively correlated with malic-acid content. Malic and citric acid, as intermediate metabolites in the tricarboxylic acid cycle, play important roles in plants, among which malic acid also participates in glycolysis and the glyoxylate cycle, as well as and other life activities (Huang et al. 2021 ). When the fruit is ripe, malic acid and citric acid are stored in vacuoles in plant cells by transport involving a wide variety of transport proteins, such as citric acid transporter proteins, the dicarboxylatetricarboxylate carrier, the vacuolar membrane dicarboxylic acid transporter protein, the tonoplast dicarboxylate transporter (TDT), and the proton pump protein. Studies have found that the main transporter of malic acid is the TDT, and overexpression of the transporter gene SlTDT, encoding the vacuole membrane in tomato, can increase the malic-acid content in fruit and reduce the citric-acid content, while the inhibition of the expression of this gene leads to decreased malic-acid content and increased citric-acid content (Liu et al. 2017 ; Shi et al. 2019 ; Zheng et al. 2021 ). Therefore, this study speculates that the diversity of organic acid types in apricot resource fruits is not only related to the ripening stage of the fruit, but also to the type of transporter proteins activated by different varieties during the ripening stage. Sugar and organic acids in fruits are the main accumulation forms of carbon assimilates in plants, and they can be interconverted through various enzymatic reactions (Aprea et al. 2017 ; Sweetman et al. 2009 ; Wu et al. 2021 ). In this study, fructose was inversely correlated with citric-acid and total-acid contents in apricot fruit. Reducing sugars such as fructose and glucose are converted to fructose 6-phosphate and glucose 6-phosphate, catalyzed by phosphokinase, thus entering the tricarboxylic acid cycle to produce citric acid (Kongjie et al. 2022). Numerous studies have shown that the accumulation of organic acids in fruits is mainly determined by the energy released by organic acid transporters and ATP hydrolysis on the vacuole membrane (Gai et al. 2024 ; Wang et al. 2021 ; Yu et al. 2021 ). As key substances in the glycolytic pathway, fructose provides a crucial energy source for intracellular life activities. Conclusions Through a deep analysis of the compositions of sugars and organic acids in apricot fruit, we have provided a solid theoretical basis for the improvement of apricot cultivation. In addition, our classification method based on sugar and organic acid characteristics not only facilitates the standardization of resources from various countries, it also promotes the effective utilization and development of apricot germplasm resources. In conclusion, this study provides important scientific data and practical guidance for the improvement of apricot fruit quality and breeding practice. Declarations Author contribution statement Chenjuan Jing and Xiaohong Wu : study conception and design. Chenjuan Jing , Duan Wang , and Zhikun Liu : data collection. Chenjuan Jing, Zhikun Liu , and Xuefeng Chen : analysis and interpretation of results, draft manuscript preparation. Chenjuan Jing : Writing–review & editing. Chenjuan Jing , Duan Wang , and Xiaohong Wu : project administration and funding acquisition. All authors reviewed the results and approved the final version of the manuscript. Acknowledgments This work was supported by Basic Research Funds of Hebei Academy of Agriculture and Forestry Sciences (No2024100202), HAAFS Science and Technology Innovation Special Project (2022KJCXZX-SGS-8), S&T Program of Hebei (21326310D) and Hebei Agriculture Research System (HBCT2024150210). Compliance with ethical standard Conflict of interest The authors declare that they have no conflict of interest. References Aprea E, Charles M, Endrizzi I, Laura C M, Betta E, Biasioli F Gasperi F (2017 ) Sweet taste in apple: the role of sorbitol, individual sugars, organic acids and volatile compounds. Sci Rep 7: 44950. Ayse D, Ozsahin, Yilmaz O (2010) Fruit sugar, flavonoid and phytosterol contents of apricot fruits ( Prunus armeniaca L. cv. Kabaasi) and antioxidant effects in the free radicals environment. Asian Journal of Chemistry 22: 6403-6412. Baccichet I, Chiozzotto R, Spinardi A, Gardana C, Bassi D, Cirilli M (2022) Evaluation of a large apricot germplasm collection for fruit skin and flesh acidity and organic acids composition. Scientia Horticulturae 294. Baccichet I, Tagliabue GA, da Silva Linge C, Tura D, Chiozzotto R, Bassi D, Cirilli M (2023) Sensory perception of citrate and malate and their impact on the overall taste in apricot ( Prunus armeniaca L.) fruits. Scientia Horticulturae 321. Caliskan O, Bayazit S, Sumbul A (2012) Fruit quality and phytochemical attributes of some apricot ( Prunus armeniaca L.) cultivars as affected by genotypes and seasons. Notulae Botanicae Horti Agrobotanici Cluj-Napoca 40: 284-294. Chen M, Chen X, Zhijuan C, Shi Z (2006). Changes of sugar and acid constituents in apricot during fruit development. Acta Horticulturae Sinica 33: 805-808. Deng W, Wang Y, Liu Z, Cheng H, Xue Y (2014) HemI: A Toolkit for Illustrating heatmaps. PLOS ONE 9, e111988. Du M, Zhu Y, Nan H, Zhou Y, Pan X (2024). Regulation of sugar metabolism in fruits. Scientia Horticulturae 326. Etienne A, Génard M, Lobit P, Mbeguié-A-Mbéguié D, Bugaud C (2013) What controls fleshy fruit acidity? A review of malate and citrate accumulation in fruit cells. Journal of Experimental Botany 64: 1451-1469. Fan XG, Zhao HD, Wang XM, Cao JK, Jiang WB (2017) Sugar and organic acid composition of apricot and their contribution to sensory quality and consumer satisfaction. Scientia Horticulturae 225: 553-560. Gai W, Yuan L, Yang F, Ahiakpa JK, Li F, Ge P, Zhang X, Tao J, Wang F, Yang Y, Zhang Y (2024) Genome-wide variants and optimal allelic combinations for citric acid in tomato. Horticulture research 11 uhae070 Gurrieri F, Audergon J-M, Albagnac G, Reich M (2001) Soluble sugars and carboxylic acids in ripe apricot fruit as parameters for distinguishing different cultivars. Euphytica 117: 183-189 Hao S, Jun Z, Li Y, Feng J, Meiling Z, Yu W (2019) Fruit scientific research in New China in the past 70 years: Apricot. Journal of Fruit Science 36: 1302-1319 Huang XY, Wang CK, Zhao YW, Sun CH, Hu DG (2021) Mechanisms and regulation of organic acid accumulation in plant vacuoles. Horticulture research 8, 227 Jing C, Feng D, Zhao Z, Wu X, Chen X (2020) Effect of environmental factors on skin pigmentation and taste in three apple cultivars. Acta Physiologiae Plantarum 42 Jing C, Ma C, Zhang J, Jing S, Jiang X, Yang Y, Zhao Z (2016) Effect of debagging time on pigment patterns in the peel and sugar and organic acid contents in the pulp of ‘Golden Delicious’ and ‘Qinguan’ apple fruit at mid and late stages of development. PLOS ONE 11, e0165050 Kong W, Cheng H, Qi T, Xue S, Xiao Z, Song W (2022) Research advanced on character of sugar accumulation and mechanism of sucrose transport in citrus fruit. Acta Horticulturae Sinica 49: 2543–2558 Li M, Li P, Ma F, Dandekar AM, Cheng L (2018) Sugar metabolism and accumulation in the fruit of transgenic apple trees with decreased sorbitol synthesis. Horticulture research 5: 60 Lijing Z, Jiyun N, Zhen Y (2015) Advances in research on sugars，organic acids and their effects on taste of fruits. Journal of Fruit Science 32: 304-312 Liu R, Li B, Qin G, Zhang Z, Tian S (2017) Identification and functional characterization of a tonoplast dicarboxylate transporter in tomato (Solanum lycopersicum). Front Plant Sci 8: 186 Liu W, Liu N, Yu X, Zhang Y, Sun M, Xu M (2010) Apricot germplasm resources and their utilization in China, 862 ed. International Society for Horticultural Science (ISHS), Leuven, Belgium: 45-50 Mei L, Zhou Y, Tian W, Yang X, Jian X, Wei Z (2021) A study on the components and characteristics of sugars and acids in 8 hybrid citrus cultivars. Journal of Fruit Science 38: 202-211 Mei C, Xue C, Zhi C, Zuo S (2006) Changes of sugar and acid constituents in apricot during fruit development. Acta Horticultrae Sinica 33: 805-808 Shi CY, Hussain SB, Yang H, Bai YX, Khan MA, Liu YZ (2019) CsPH8, a P-type proton pump gene, plays a key role in the diversity of citric acid accumulation in citrus fruits Plant science : an international journal of experimental plant biology 289, 110288 Shuo L, You-chun L, Ning L, Yu-ping Z, Qiu-ping Z, Ming X, Yu-jun Z Wei-sheng L (2016) Sugar and organic acid components in fruits of plum cultivar resources of genus prunus. Scientia Agricultura Sinica 49: 3188-3198 Sweetman C, Deluc LG, Cramer GR Ford, CM Soole KL (2009) Regulation of malate metabolism in grape berry and other developing fruits. Phytochemistry 70: 1329-1344 Wang C, Xiang Y, Qian D (2021) Current progress in plant V-ATPase: from biochemical properties to physiological functions. J Plant Physiol Wang Y, Zhang J, Sun H, Ning N, Yang L (2011) Construction and evaluation of a primary core collection of apricot germplasm in China. Scientia Horticulturae 128: 311-319 Wu S, Li M, Zhang C, Tan Q, Yang X, Sun X, Pan Z, Deng X, Hu C (2021) Effects of phosphorus on fruit soluble sugar and citric acid accumulations in citrus. Plant Physiol Biochem 160: 73-81 Yan L, Jian N, Qing C (2007) Review on the factors to influence on the metabolism of sugars and acids in peach fruit. Chinese Agricultural Science Bulletin 23: 212-216 Yu JQ, Gu KD, Sun CH, Zhang QY, Wang JH, Ma FF, You CX, Hu DG, Hao YJ (2021) The apple bHLH transcription factor MdbHLH3 functions in determining the fruit carbohydrates and malate. Plant Biotechnology Journal 19: 285-299 Zhang C, Geng Y, Liu H, Wu M, Bi J, Wang Z, Dong X, Li X (2023) Low-acidity ALUMINUM-DEPENDENT MALATE TRANSPORTER4 genotype determines malate content in cultivated jujube. Plant Physiol 191: 414-427 Zhang LL, Liu WS, Liu YC, Liu N, Zhang YP (2010) Measurement of sugars,organic acids in 5 apricot cultivars by high performance liquid chromatography. Journal of Fruit Science 27: 119-123 Zheng B, Zhao L, Jiang X, Cherono S, Liu J, Ogutu C, Ntini C, Zhang X, Han Y (2021) Assessment of organic acid accumulation and its related genes in peach. Food Chem 334, 127567 Supplementary Files supppfig01.tif supppfig02.tif supplementaryinformation.docx Cite Share Download PDF Status: Under Review Version 1 posted Reviewers agreed at journal 13 Sep, 2025 Reviewers invited by journal 19 Feb, 2025 Editor assigned by journal 17 Feb, 2025 First submitted to journal 13 Feb, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6028777","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":417886329,"identity":"84f61c1e-7d6d-444b-98b8-8949808acea8","order_by":0,"name":"Chenjuan Jing","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA3ElEQVRIiWNgGAWjYBACxmYQ0QDBDB8MbOxI08I4oyAtmUirGiA0M8+HQzA2bsDcznv4xc8dNnnMM5KfPbYxOMDMwH746Ab8DuNLs+w9k1bMOCPN3DjH4A4fA09a2g38WnjMjBnbDic2zkgwk84xeMbMIMFjRoyW/0At6d+kLQwOMzYQocX4MWPbAaCWHDNpBiK1mDH2tiUnNva8KZPsMUhLZiPkF8P+M8YffrbZJW5sT98m8eOPjR0/++Fj+LU0MLBJQBkQwIZPOQjIA6PmA5QxCkbBKBgFowA7AABYL0qFosl91AAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0002-0437-5091","institution":"Hebei Academy of Agriculture and Forestry Sciences","correspondingAuthor":true,"prefix":"","firstName":"Chenjuan","middleName":"","lastName":"Jing","suffix":""},{"id":417886330,"identity":"7b9d5faa-d86f-4cf3-8667-de84a82fbd6a","order_by":1,"name":"Duan Wang","email":"","orcid":"","institution":"Hebei Academy of Agriculture and Forestry Sciences","correspondingAuthor":false,"prefix":"","firstName":"Duan","middleName":"","lastName":"Wang","suffix":""},{"id":417886331,"identity":"f30de27a-a850-4b45-908b-472f5bfc885f","order_by":2,"name":"Zhikun Liu","email":"","orcid":"","institution":"Hebei Academy of Agriculture and Forestry Sciences","correspondingAuthor":false,"prefix":"","firstName":"Zhikun","middleName":"","lastName":"Liu","suffix":""},{"id":417886332,"identity":"b334ef3a-10cb-403e-ae17-02af4b0b537c","order_by":3,"name":"Xuefeng Chen","email":"","orcid":"","institution":"Hebei Academy of Agriculture and Forestry Sciences","correspondingAuthor":false,"prefix":"","firstName":"Xuefeng","middleName":"","lastName":"Chen","suffix":""},{"id":417886333,"identity":"c79bb98d-4b89-4362-8dae-dc36a522aa4b","order_by":4,"name":"Xiaohong Wu","email":"","orcid":"","institution":"Hebei Academy of Agriculture and Forestry Sciences","correspondingAuthor":false,"prefix":"","firstName":"Xiaohong","middleName":"","lastName":"Wu","suffix":""}],"badges":[],"createdAt":"2025-02-14 08:35:33","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6028777/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6028777/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":76835433,"identity":"645c8959-f91a-488b-b8ce-5561dad29676","added_by":"auto","created_at":"2025-02-21 09:11:50","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":77651,"visible":true,"origin":"","legend":"\u003cp\u003eDistribution of sugars in the ripening fruits of the natural apricots population. There are 322 materials in the population. A, shows the frequency distribution histogram of sugars in the apricot fruit of the natural apricot population, the horizontal coordinate indicates the concentration of sugars content (mg/g FW), and the ordinate is the frequency of sugar contents (mg/g FW). B, the boxplot shows the distribution of sugars contents (mg/g FW) in this population. And two-years measurements for 322 accessions were averaged.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6028777/v1/9d2858f3238b3c7a7761dbf7.png"},{"id":76835430,"identity":"3f20d24f-4ef1-47ba-b9f8-98558d97bbfd","added_by":"auto","created_at":"2025-02-21 09:11:50","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":79591,"visible":true,"origin":"","legend":"\u003cp\u003eDistribution of organic-acids in the ripening fruits of the natural apricots population. There are 322 materials in the population. A, shows the frequency distribution histogram of organic-acid content (mg/g FW) in the apricot fruit of the natural apricot population, the horizontal coordinate indicates the concentration of organic-acids, and the ordinate is the frequency of organic-acid contents (mg/g FW). B, the boxplot shows the distribution of organic-acid contents (mg/g FW) in this population. And two-years measurements for 322 accessions were averaged.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6028777/v1/74264feee543a0046d4f0ff3.png"},{"id":76835696,"identity":"fb8df0e8-134d-4e36-b1f0-5ae3f6444380","added_by":"auto","created_at":"2025-02-21 09:19:50","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":102378,"visible":true,"origin":"","legend":"\u003cp\u003eDistribution trends for sugars and organic acids in apricot germplasm fruits. A and C depict the absolute content distribution of sugars and organic-acid contents (mg/g FW) within germplasm fruits. The horizontal axis serves to represent each individual resource (cultivars), with the vertical axis indicating the content (mg/g FW) of these substances. Meanwhile, B and D showcase the relative content distribution. In this context, the horizontal axis remains dedicated to each resource (cultivars), and the vertical axes clearly display the proportions of different sugar and organic-acid contents in relation to their respective total amounts.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6028777/v1/ba3c42c23ed0f6f4d142f7db.png"},{"id":76837032,"identity":"79fbd4fb-066c-4f45-b5f8-d228bab3f50b","added_by":"auto","created_at":"2025-02-21 09:27:50","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":406291,"visible":true,"origin":"","legend":"\u003cp\u003eCluster-analysis results for (A) sugars and (B) organic acids in apricot resource fruits. Mature apricot fruits contain primarily sucrose and glucose as main sugars, and malic and citric acids as principal organic acids. Cluster analysis of sugar and organic acid profiles reveals two sugar groups and three organic-acid groups, respectively. The figure uses color gradients: green (low), light orange (medium), and dark orange (high) to denote nutritional compound levels.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6028777/v1/69e8a06f0eecc289d0fd1cb7.png"},{"id":76834389,"identity":"b7619d40-02cd-4805-b1fc-d50776eec3ab","added_by":"auto","created_at":"2025-02-21 09:03:50","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":59511,"visible":true,"origin":"","legend":"\u003cp\u003eG/S and M/C ratio distributions for apricot resource fruits (M/C, the ratio of malic acid and citric acid; G/S, the ratio of glucose and sucrose). The glucose-to-sucrose (G/S) and malic acid-to-citric acid (M/C) ratios in 64 apricot germplasm fruits were logarithmically transformed (base 2). In Figure 5A, the minimum Log\u003csub\u003e2\u003c/sub\u003e (G/S) reached −4.7 (sucrose content ~25.7 times glucose), while the maximum Log\u003csub\u003e2\u003c/sub\u003e (G/S) was 1.6 (glucose ~ 3.2 times sucrose), categorizing the fruits into glucose-dominant and sucrose-dominant types. Figure 5B showed extreme M/C ratios ranging from 0.82 (Log\u003csub\u003e2\u003c/sub\u003e (M/C) = −2.6, citric acid dominance) to 47.8 (Log\u003csub\u003e2\u003c/sub\u003e (M/C) = 5.5, malic acid ~40-fold higher), demonstrating distinct malic acid-dominant and citric acid-dominant apricot germplasm types.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-6028777/v1/a8ad2ad018d6c32a88bf9372.png"},{"id":76834394,"identity":"ca3ae128-efec-43ec-9817-e6e4492eb717","added_by":"auto","created_at":"2025-02-21 09:03:50","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":62720,"visible":true,"origin":"","legend":"\u003cp\u003eDevelopment trends for sugar contents in apricot fruits. (A and B) Two-sugar types ‘Shunpingganzhi’ and ‘Hamazui’. (C and D) Suc-types ‘Qingmisha’ and ‘Lanzhoudajiexing’ (DAB, days after bloom). All varieties were sampled weekly starting 28 days after full bloom. The sugars contents in peeled flesh was analyzed using high-performance liquid chromatography (HPLC). Data were collected over three consecutive growing seasons (2021-2022 and 2023), with average values calculated from the triennial measurements.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-6028777/v1/24586958e55b533ec9dd51d5.png"},{"id":76835435,"identity":"feb0415a-2d48-49bf-a02e-723fdab03602","added_by":"auto","created_at":"2025-02-21 09:11:50","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":229321,"visible":true,"origin":"","legend":"\u003cp\u003eDevelopment trends for acid contents in apricot fruit. (A and B) Mal-type apricot resources. (C and D) Cit-type apricot resources. (D and F) Two-acid-type resources (DAB, days after bloom). All cultivars underwent weekly sampling commencing 28 days after full bloom. Organic-acid contents in peeled flesh was quantified using high-performance liquid chromatography (HPLC). Data were collected over three consecutive growing seasons (2021-2022 and 2023), with results presented as mean values ± standard error (error bars) derived from triplicate annual measurements. Significant differences among treatments on each sampling date were determined by Tukey’s test, \u003cem\u003eP \u003c/em\u003e\u0026lt; 0.05.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-6028777/v1/823383102f277665f3db68c4.png"},{"id":76837263,"identity":"28a0c1ad-f82d-4bd0-a121-fc46c79d364c","added_by":"auto","created_at":"2025-02-21 09:35:51","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1795235,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6028777/v1/6ca24740-194a-4055-bd7e-cf1de9c3b489.pdf"},{"id":76835434,"identity":"86505371-b35e-4a9f-a7c1-fb349deaffab","added_by":"auto","created_at":"2025-02-21 09:11:50","extension":"tif","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":1772564,"visible":true,"origin":"","legend":"","description":"","filename":"supppfig01.tif","url":"https://assets-eu.researchsquare.com/files/rs-6028777/v1/03ec4075ab7cd2130cece925.tif"},{"id":76834400,"identity":"38612f6f-e78d-402a-968e-f8f392eb8a0a","added_by":"auto","created_at":"2025-02-21 09:03:50","extension":"tif","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":1652288,"visible":true,"origin":"","legend":"","description":"","filename":"supppfig02.tif","url":"https://assets-eu.researchsquare.com/files/rs-6028777/v1/4e435971ce15b652dd9d2416.tif"},{"id":76834404,"identity":"a592c567-8515-4af2-955e-691f6f7fe180","added_by":"auto","created_at":"2025-02-21 09:03:50","extension":"docx","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":3303931,"visible":true,"origin":"","legend":"","description":"","filename":"supplementaryinformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-6028777/v1/47ace0e32a77217ebfc6c7d2.docx"}],"financialInterests":"","formattedTitle":"Distribution and developmental characteristics of sugars and organic acids in fresh apricots","fulltext":[{"header":"Introduction","content":"\u003cp\u003eApricot (\u003cem\u003ePrunus armeniaca\u003c/em\u003e L.) is highly popular with consumers for its early ripening, excellent flavor, and nutritional value, making it one of the most important fruit crops in China (Liu et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Wang et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). In 2016, the total apricot-cultivation area for the fresh market and processing in China exceeded 360,000 hectares, with a total yield of 2,700,000 tons (Haoyuan et al. 2019). Driven by consumer demand, higher-quality apricots have a greater commodity value. Specifically, sweet apricot varieties with low acidity are more favored by consumers and thus have greater market value. Conversely, sour-tasting apricots have limited economic value.\u003c/p\u003e \u003cp\u003eThe taste of a fruit is primarily influenced by the types and contents of sugars and organic acids therein. Sucrose and malic acid are the main sugar and organic acid, respectively, in apples, accounting for over 90% of the total sugar and total acid contents (Jing et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). In citrus fruits, the sugar contents range from 60 to 130 mg/g fresh weight (FW), with that of sucrose typically accounting for ~\u0026thinsp;50% of the total. The organic-acid contents in citrus fruits fall in the range 6\u0026ndash;11 mg/g FW, with malic and citric acid being most abundant (Mei et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). In peaches, which are important drupe fruits, the sugar contents range from 55 to 160 mg/g FW, with fructose and glucose being dominant in the young fruit and sucrose becoming dominant upon maturity. The organic-acid contents in peaches fall in the range 4\u0026ndash;28 mg/g FW, with malic and citric acids being the main components at maturity, the specific contents of which vary depending on cultivar (Yanping et al. 2007). Plums, another highly cultivated variety of drupe fruits, are mainly Chinese species. Sucrose is the main sugar in plums with a content range of 24.8\u0026ndash;152 mg/g FW, accounting for over 80% of the total sugars. Malic acid is the main organic acid in plums, with a content range of 11.8\u0026ndash;66.38 mg/g FW (Shuo et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eApricots are also drupe fruits, and their sugar contents range from 31 to 130 mg/g FW. The main sugars in apricots are glucose, sucrose, fructose, and sorbitol, among which sucrose is the dominant component, accounting for over 60% of the total sugar, followed by glucose, while fructose and sorbitol contents are relatively low, accounting for less than 30% of the total. Therefore, apricot fruits are classified as sucrose-type fruits (Ayse et al. 2010; Fan et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). The organic-acid contents of apricot fruits range from 9.5 to 54 mg/g FW, mainly comprising quininic, malic, and citric acids. Of these, quininic acid has the lowest content, accounting for just 2\u0026ndash;12% of the total organic acid, while the combined contents of malic and citric acids account for over 90% of the total organic acids. Currently, the organic acids in apricots classify them as malic-acid-type fruits (Etienne et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Zhang et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). However, existing research on sugars and acids in apricot fruits may be subject to inaccuracy due to the limited number of varieties typically studied. Furthermore, there are currently no reported studies on the changes in sugar and organic-acid contents during apricot fruit development(Baccichet et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAccordingly, this study employed high-performance liquid chromatography (HPLC) to conduct a detailed analysis of the sugar and organic-acid contents and distribution ratios in mature apricot fruits from a natural population of 332 common apricot seedlings and 64 germplasm resources (local varieties or introduced varieties). Through classification and screening, we selected eight apricot varieties with outstanding characteristics, including sucrose-type and reducing-sugar-type specimens as well as malic-acid-type, citric-acid-type, and two-acid-type fruits. Detailed analysis of these specimens revealed the changes in their sugar and organic-acid contents during development. In doing so, this study provides data support for improving fruit quality, as well as elucidating the mechanisms by which sugars and organic acids are accumulated and metabolized. Overall, this work provides a scientific basis for the breeding of high-quality apricot varieties with high sugar and/or low acid contents.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eNatural seedling population\u003c/h2\u003e \u003cp\u003eThis population consisted of 332 seedling materials, which were planted in 2009 at the Shijiazhuang Fruit Research Institute (SFRI-HAAFS; Shijiazhuang, Hebei Province, China, 38\u0026deg; 7' N, 114\u0026deg; 32' E). The trees were planted in north-south rows with a density of 1 m \u0026times; 2 m and received routine management for irrigation and pest control. Samples were collected in May\u0026ndash;June 2022, i.e., during fruit ripening. Since each tree represented a unique material, 15 fruits were randomly picked from the outer perimeter of each tree. These fruits were divided into three replicates, with five fruits per replicate. The samples were frozen for storage prior to analysis.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eGermplasm resources\u003c/h3\u003e\n\u003cp\u003eThe apricot germplasm resources were introduced to the germplasm repository at the Shijiazhuang Fruit Research Institute at different times. The rootstock used was \u003cem\u003eArmeniaca sibirica\u003c/em\u003e, and the planting density was 3 m \u0026times; 4 m, with trees planted in north-south rows. Based on previous investigations of growth habits and fruit taste in combination with comprehensive evaluations of fruit appearance and flavor, 64 outstanding apricot germplasm resources were selected (Supplementary Table\u0026nbsp;1). Samples were collected during fruit ripening for the determination of sugar and organic-acid type and content. Additionally, six varieties, \u0026lsquo;Qingmisha\u0026rsquo;, \u0026lsquo;Hamazui\u0026rsquo;, \u0026lsquo;Zhenzhuyou\u0026rsquo;, \u0026lsquo;Jinhui\u0026rsquo;, \u0026lsquo;Shunpingganzhi\u0026rsquo;, and \u0026lsquo;Meishuo\u0026rsquo;, were selected from the resources as experimental materials. Samples were collected every week from 20 days after flowering until fruit ripening. Fifteen apricot fruits were randomly picked from the outer perimeter of each tree, then divided into three replicates with five fruits per replicate.\u003c/p\u003e\n\u003ch3\u003eDetermination of sugars and organic acids\u003c/h3\u003e\n\u003cp\u003eThe identification and characterization of sugars and organic acids (sucrose, glucose, fructose, sorbitol, malic acid, citric acid, and quininic acid) were conducted using HPLC techniques as previously described (Jing et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Analysis of sugars was performed using a system comprising a Waters 2695 pump, a Multospher\u0026reg; Sugar 5u column (250 mm \u0026times; 4.6 mm \u0026times; 5 \u0026micro;m; Waters, USA), and a 2414 refractive index (RI) detector. The organic acids were determined using a system that comprised a RIGOL L-3000 pump, an HP-C18-AQ column (250 mm \u0026times; 4.6 mm, 5 \u0026micro;m), and a photodiode array detector. The mobile phase consisted of 0.1 M phosphoric acid buffer (pH 3.1) with a flow rate of 1.0 mL/min at 30\u0026deg;C, and detection was carried out at 210 nm (Jing et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e\n\u003ch3\u003eStatistical data analysis\u003c/h3\u003e\n\u003cp\u003eData processing and graph plotting were performed using Microsoft Excel 2007. Correlation analysis was conducted with IBM SPSS Statistics 19 (SPSS Inc., Armonk, NY, USA), and least-significant-difference analysis was used to establish the significance of differences between samples.\u003c/p\u003e \u003cp\u003eHistograms and box plots were created using Minitab 16. Clustered heatmaps were generated using HemI 1.0. Hierarchical clustering and heat-map analysis of apricot cultivars and parameters were performed using squared Euclidean distance and average linkage clustering algorithms (Deng et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eDistribution characteristics of sugars and organic acids in fruits from natural apricot populations\u003c/h2\u003e \u003cp\u003eIn the apricot fruits, the distributions of fructose and sucrose contents are close to normal population. Although the contents of these sugars are mainly controlled by multiple minor-effect genes and show quantitative traits, there are some major gene effects at play. In contrast, the distribution of fructose content is more inclined to show quality traits, with control by multiple minor-effect genes playing an auxiliary role. The mean fructose content is 12.34 mg/g FW with a low variance value of 25.22 mg/g FW. The fructose contents range from 3.71 to 43.79 mg/g FW, being mainly distributed in the range 7\u0026ndash;15 mg/g FW (71.3% of the population).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eGlucose content of the nature apricot fruits population averaged 13.55 mg/g FW with a minimum of 3.02 mg/g FW up to a maximum of 51.37 mg/g FW. The glucose contents are mainly distributed at 5\u0026ndash;13 mg/g FW, accounting for 59.82% of the total sugar. Sucrose, as the main sugar component in apricot fruit, average 33.28 mg/g FW and show the most variance (228.151 mg/g FW). The sucrose contents range between 0.009 and 88.84 mg/g FW, with 64.95% of the population distributed in the 22.5\u0026ndash;47.5 mg/g FW range.\u003c/p\u003e \u003cp\u003eThe total-sugar content of apricot fruit is the sum of the contents of fructose, glucose, and sucrose, and its distribution is close to normal. The total sugar contents fall in the range 16.97\u0026ndash;126.36 mg/g FW, with a mean content of 58.65 mg/g FW. The total sugar contents are mainly distributed at 27.5\u0026ndash;82.5 mg/g FW, accounting for 87.92% of the total (Supplementary Table\u0026nbsp;2).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eApricot fruits contain much less quininic acid than malic and citric acids. The three organic-acid contents distribution tend to be normal, but they also show the characteristics of data discontinuity. Therefore, the contents of these three organic acids are quantitative traits controlled by micro-polygenes, and they are also regulated by certain main genes, showing the characteristics of quality traits.\u003c/p\u003e \u003cp\u003eAmong them, quininic acid is the least abundant organic acid in apricot fruit. At its lowest content, it is difficult to detect, while the highest content is 5.61 mg/g FW. In the natural apricot group, the average quinine-acid content is 1.05 mg/g FW, and it is mainly concentrated in the range 0.625\u0026ndash;1.625 mg/g FW, accounting for 67.69%.\u003c/p\u003e \u003cp\u003eThe malic-acid contents for this population average 9.13 mg/g FW with a distribution range of 1.6\u0026ndash;22.4 mg/g FW, where the content is mainly concentrated in the 2.5\u0026ndash;13.5 mg/g FW range (80.97% of the total population).\u003c/p\u003e \u003cp\u003eFor citric acid, the mean content in this population is 8.09 mg/g FW (Supplementary Table\u0026nbsp;2), and the content distribution ranges from 0.48 to 21.0 mg/g FW. The main concentrated distribution area is 1.5\u0026ndash;12.5 mg/g FW, which accounts for 72.51% of the population.\u003c/p\u003e \u003cp\u003eThe total-acid content is the sum of the three organic acids above, and although their distributions tend to be normal, the continuity of the data is relatively poor. This suggests that the regulation of total-acid content involves both major genes and multiple minor-effect genes. The total organic-acid contents in the apricot fruit of this population are 8.54\u0026ndash;28.57 mg/g FW and the mean value is 18.25 mg/g FW. The contents are mainly concentrated in the 12.5\u0026ndash;21.5 mg/g FW interval, accounting for 79.15%.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eDistribution of sugars and organic acids in the fruits of apricot germplasm resources\u003c/h3\u003e\n\u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Taba\" border=\"1\"\u003e \u003ccolgroup cols=\"9\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"8\" nameend=\"c8\" namest=\"c1\"\u003e \u003cp\u003eTable\u0026nbsp;1 Classes and contents of sugars and organic acids in apricot resource fruits\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"1\" nameend=\"c9\" namest=\"c9\"\u003e\u0026nbsp;\u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eN\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003emean values\u003c/p\u003e \u003cp\u003e(mg/g FW)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003estandard deviation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003ecoefficient of variation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eminimum\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003emaximum\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e \u003cp\u003eskewness\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFructose\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e64\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e12.71\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e6.28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e49.40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e2.94\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e29.70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e \u003cp\u003e0.30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGlucose\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e64\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e29.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e15.59\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e53.39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e3.59\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e70.43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e \u003cp\u003e0.70\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSucrose\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e64\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e41.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e13.95\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e33.87\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e10.72\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e73.73\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e \u003cp\u003e0.43\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal sugar\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e64\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e82.70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e22.60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e27.33\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e38.48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e138.78\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e \u003cp\u003e0.30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eQuininic acid\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e64\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.83\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.63\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e76.13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e4.83\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e \u003cp\u003e4.28\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMalic acid\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e64\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6.14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e49.60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1.60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e13.60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e \u003cp\u003e0.49\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCitric acid\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e64\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5.62\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4.99\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e88.66\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e16.84\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e \u003cp\u003e0.64\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal acid\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e64\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e12.60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3.87\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e30.72\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e4.091\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e20.93\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e \u003cp\u003e0.24\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"8\" nameend=\"c8\" namest=\"c1\"\u003e \u003cp\u003eSixty-four apricot resources, each with 15 mature fruits, are randomly divided into 3 groups. This leads to a total of 192 replicates for all the resources. In these independent replicates, significant differences among treatments on each sampling date are identified using Tukey's test with a significance level of \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05. And two-years measurements for 64 resources were averaged.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"1\" nameend=\"c9\" namest=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe fructose contents of the resource fruit fall in the range 2.94\u0026ndash;29.70 mg/g FW. Compared with the natural group, the fructose content is slightly lower, but it is still within the same range. The mean fructose content for the resource fruit is 12.71\u0026thinsp;\u0026plusmn;\u0026thinsp;0.80 mg/g FW, which is comparable to the natural population average.\u003c/p\u003e \u003cp\u003eIn terms of organic-acid content, the quininic-acid content range for the fruits of the apricot resource group is 0.25\u0026ndash;4.83 mg/g FW, which coincides with the content range for the natural population. However, the average quininic-acid content in this population is 0.83\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08 mg/g FW, which is lower than that for the natural population.\u003c/p\u003e \u003cp\u003eSimilarly, the malic-acid contents for the apricot resource group are in the 1.60\u0026ndash;13.60 mg/g FW range, which is within the content range of the natural group. However, the average value is 6.14\u0026thinsp;\u0026plusmn;\u0026thinsp;0.38 mg/g FW, which is relatively low compared with the natural population.\u003c/p\u003e \u003cp\u003eThis population has a wide range of citric-acid contents at 0.1\u0026ndash;16.84 mg/g FW, with its lowest and highest contents being beyond the corresponding range for the natural population. However, the average content is 5.62\u0026thinsp;\u0026plusmn;\u0026thinsp;0.62 mg/g FW, which is lower than the average for the natural population.\u003c/p\u003e \u003cp\u003eFor total-acid contents, the distribution range for the apricot resource group is 4.09\u0026ndash;20.93 mg/g FW, covering both the lowest and highest contents seen in this study. The average total-acid content is 12.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.48 mg/g FW, which is lower than that for the natural population (Table\u0026nbsp;1).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn the germplasm fruit, the absolute contents of fructose are the lowest (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB), ranging from 2.17\u0026ndash;35.48% and having relatively little influence on the total-sugar content. The distribution trend is not affected by the glucose and sucrose contents. The content distributions for glucose and sucrose show certain differences: the absolute content of glucose directly affects the total-sugar content of apricot fruit, and its relative content is distributed between 3.66% and 59.82%. In contrast, the absolute content of sucrose is relatively evenly distributed, with its relative contents ranging from 18.97\u0026ndash;96.20%, making it the main sugar component for germplasm resources (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB). Furthermore, some correlation may be found between the relative content of sucrose and the content of glucose.\u003c/p\u003e \u003cp\u003eThe germplasm fruits have the lowest quinine-acid contents and the smallest proportions, ranging from 1.60\u0026ndash;24.58%. However, the distributions of malic and citric acids are different, with their relative contents ranging between 10.22\u0026ndash;94.37% and 1.91\u0026ndash;86.28%, respectively. Furthermore, in some apricot resources, the proportions of malic and citric acids are quite different. Whether from the perspective of absolute organic-acid content or relative content, there are some apricot resources with high proportions of malic acid and some with high proportions of citric acids. Therefore, we initially divided these resources into malic-acid-dominant type (mal-type) and citric-acid-dominant type (cit-type) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eC and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eD). And there were similar distribution trends of sugars and organic acids in natural apricots group fruits (Supplementary Fig.\u0026nbsp;1 and Supplementary Fig.\u0026nbsp;2).\u003c/p\u003e\n\u003ch3\u003eClassification of fruit sugars and organic acids in apricot germplasm resources\u003c/h3\u003e\n\u003cp\u003e \u003c/p\u003e \u003cp\u003eBy analyzing the absolute and relative distribution characteristics of sugars and organic acids in apricot resource fruits, we clustered them by glucose and sucrose contents and malic and citric acid contents. The results show that, based on the main sugars contents, the resources can be clustered into four categories: Class I resources have mainly glucose contents with relatively high total-sugar contents; Class II resources have roughly equal glucose and sucrose contents along with high total-sugar contents; Class III resources have high sucrose contents; and Class IV resources have roughly equal glucose and sucrose contents but low total-sugar contents (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA).\u003c/p\u003e \u003cp\u003eIn terms of organic acids, the resources can be divided into two categories: Class I resources are high in citric acid, and their total-acid contents are generally high; the other category is mainly malic acid and contains many resources with low acid contents (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. B).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eWe identified 53 apricot resources with a ratio of glucose and sucrose (G/S) in base 2 log transformation, i.e., ∣log\u003csub\u003e2\u003c/sub\u003e (G/S)∣, lower than 1.5. When G/S is between 0.3 and 3, the fruit glucose and sucrose contents are between 25% and 75%, so we classify such fruit as two-sugar-accumulating type (two-sugar type). Only \u0026lsquo;Mingxing No.1\u0026rsquo; is classified as glucose-dominant type (glu-type), with its value of log\u003csub\u003e2\u003c/sub\u003e (G/S) being 1.66. There are 10 sucrose-dominant type (suc-type) resource varieties, especially \u0026lsquo;Qingmisha\u0026rsquo; (G/S\u0026thinsp;=\u0026thinsp;1:25.7), \u0026lsquo;Yuzhouhong\u0026rsquo; (G/S\u0026thinsp;=\u0026thinsp;1:25.3), \u0026lsquo;Qinxing\u0026rsquo; (G/S\u0026thinsp;=\u0026thinsp;1:16.5), and \u0026lsquo;Jingcuihong\u0026rsquo; (G/S\u0026thinsp;=\u0026thinsp;1:6.4). Their values of log\u003csub\u003e2\u003c/sub\u003e (G/S) are lower than \u0026minus;\u0026thinsp;2, meaning that the sucrose contents of these fruits are more than six-times their glucose contents, so they are classified as extreme sucrose resources (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eA).\u003c/p\u003e \u003cp\u003eUpon further analysis of the malic acid to citric acid (M/C) ratios in apricot fruits, we found that when ∣log\u003csub\u003e2\u003c/sub\u003e (M/C)∣ \u0026le; 1, the ratio of malic acid to citric acid is between 0.5 and 2, so they are classified as two-acid-accumulating type (two-acid type) resources. A total of 16 resources were classified as such, including \u0026lsquo;Meishuo\u0026rsquo;, \u0026lsquo;Shunpingganzhi\u0026rsquo;, \u0026lsquo;Shajinhong No1\u0026rsquo;, and 9-D1, whose values of log\u003csub\u003e2\u003c/sub\u003e (M/C) are all close to zero, indicating that the contents of malic acid and organic acid in the fruits of these varieties are equivalent (Supplementary Table\u0026nbsp;3).\u003c/p\u003e \u003cp\u003eThere are 27 resources for which log\u003csub\u003e2\u003c/sub\u003e (M/C)\u0026thinsp;\u0026gt;\u0026thinsp;1, i.e., their M/C ratios are greater than 2, which we classify as a malic-acid-dominant type (mal-type) resource. Among these resources, there are 19 with log\u003csub\u003e2\u003c/sub\u003e (M/C)\u0026thinsp;\u0026gt;\u0026thinsp;2, especially \u0026lsquo;Maohong\u0026rsquo; (M/C\u0026thinsp;=\u0026thinsp;32:1), \u0026lsquo;Jingcuihong\u0026rsquo; (M/C\u0026thinsp;=\u0026thinsp;36.8:1), \u0026lsquo;Jingxianghong\u0026rsquo; (M/C\u0026thinsp;=\u0026thinsp;38.2:1), \u0026lsquo;Hamazui\u0026rsquo; (M/C\u0026thinsp;=\u0026thinsp;39.7:1), \u0026lsquo;Lanzhoudajie\u0026rsquo; (M/C\u0026thinsp;=\u0026thinsp;47.8:1), and \u0026lsquo;Wanbai\u0026rsquo; (M/C\u0026thinsp;=\u0026thinsp;342.5:1), that have log\u003csub\u003e2\u003c/sub\u003e (M/C) values greater than 5.\u003c/p\u003e \u003cp\u003eThere are 21 resources with log\u003csub\u003e2\u003c/sub\u003e (M/C) values\u0026thinsp;\u0026lt;\u0026thinsp;1, that is, their M/C ratios are less than 0.5, which we classify as a citric-acid-dominant type (cit-type). The fruits with log\u003csub\u003e2\u003c/sub\u003e (M/C)\u0026thinsp;\u0026lt;\u0026thinsp;\u0026minus;\u0026thinsp;2 include \u0026lsquo;Jinhui\u0026rsquo; (M/C\u0026thinsp;=\u0026thinsp;1:8.4), \u0026lsquo;Kate\u0026rsquo; (M/C\u0026thinsp;=\u0026thinsp;1:7.1), \u0026lsquo;Dailing\u0026rsquo; (M/C\u0026thinsp;=\u0026thinsp;1:6.1), \u0026lsquo;Jinshou\u0026rsquo; (M/C\u0026thinsp;=\u0026thinsp;1:6), \u0026lsquo;Zihe\u0026rsquo; (M/C\u0026thinsp;=\u0026thinsp;1:5.2), \u0026lsquo;Mingxing\u0026rsquo; (M/C\u0026thinsp;=\u0026thinsp;1:5), \u0026lsquo;Daguo\u0026rsquo; (M/C\u0026thinsp;=\u0026thinsp;1:4.7), \u0026lsquo;Sungold\u0026rsquo; (M/C\u0026thinsp;=\u0026thinsp;1:4.7) and \u0026lsquo;Zhenzhuyou\u0026rsquo; (M/C\u0026thinsp;=\u0026thinsp;1:4.4) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eB and Supplementary Table\u0026nbsp;3).\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Correlation analysis of sugars and organic acids in apricot fruits\u003c/h2\u003e \u003cp\u003eThere is a complex interconversion relationship between sugars and organic acids within the fruit. Not only can different kinds of sugars and organic acids transform with each other, their roles and contributions in the life activities of the fruit may also vary. The results of correlation analysis revealed that fructose had highly significant positive correlations with glucose, total sugar, citric acid, total acid, and glucose/sucrose (\u003cem\u003er\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.572, 0.510, 0.448, 0.453, 0.583; \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01) and a significant negative correlation with sucrose (\u003cem\u003er\u003c/em\u003e\u0026thinsp;=\u0026thinsp;\u0026minus;\u0026thinsp;0.270, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05).\u003c/p\u003e \u003cp\u003eThere is a very significant positive correlation between glucose and total sugar, glucose/sucrose, and sugar/acid (\u003cem\u003er\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.811, 0.800, 0.529; \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01). Sucrose shows very significant positive correlations with total sugar and sugar/acid (\u003cem\u003er\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.476, 0.475; \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01) and a very significant negative correlation with glucose/sucrose (\u003cem\u003er\u003c/em\u003e\u0026thinsp;=\u0026thinsp;\u0026minus;\u0026thinsp;0.558, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01), and a significant negative correlation with total acid (\u003cem\u003er\u003c/em\u003e\u0026thinsp;=\u0026thinsp;\u0026minus;\u0026thinsp;0.286, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Furthermore, total-sugar content shows very significant positive correlations with glucose/sucrose and glucose/acid (\u003cem\u003er\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.382, 0.630; \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01).\u003c/p\u003e \u003cp\u003eIn terms of organic acids, citric acid shows significant negative correlations with quininic acid and malic acid/citric acid (\u003cem\u003er\u003c/em\u003e\u0026thinsp;=\u0026thinsp;\u0026minus;\u0026thinsp;0.261, \u0026minus;\u0026thinsp;0.289; \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) and very significant negative correlations with malic acid and sugar/acid ratio (\u003cem\u003er\u003c/em\u003e\u0026thinsp;=\u0026thinsp;\u0026minus;\u0026thinsp;0.598, \u0026minus;\u0026thinsp;0.457; \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01). However, there is a very significant positive correlation between citric-acid content and total-acid content (\u003cem\u003er\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.795, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01). Total-acid content had highly significant negative correlations with malic acid/citric acid and sugar/acid (\u003cem\u003er\u003c/em\u003e\u0026thinsp;=\u0026thinsp;\u0026minus;\u0026thinsp;0.352, \u0026minus;\u0026thinsp;0.728; \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01), and a significant positive correlation was found between malic acid/citric acid and sugar/acid (\u003cem\u003er\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.290, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) (Table\u0026nbsp;2).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Tabb\" border=\"1\"\u003e \u003ccolgroup cols=\"12\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c12\" colnum=\"12\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"11\" nameend=\"c11\" namest=\"c1\"\u003e \u003cp\u003eTable\u0026nbsp;2 Results of correlation analysis for sugars and acids\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"1\" nameend=\"c12\" namest=\"c12\"\u003e\u0026nbsp;\u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFructose\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eGlucose\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSucrose\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eTotal\u003c/p\u003e \u003cp\u003esugar\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eQuininic\u003c/p\u003e \u003cp\u003eacid\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eMalic\u003c/p\u003e \u003cp\u003eacid\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eCitric\u003c/p\u003e \u003cp\u003eacid\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eTotal\u003c/p\u003e \u003cp\u003eacid\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eMalic acid/\u003c/p\u003e \u003cp\u003eCitric acid\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e \u003cp\u003eSugars/\u003c/p\u003e \u003cp\u003eacids\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFructose\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.572\u003csup\u003e**\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-0.270\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.510\u003csup\u003e**\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-0.194\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-0.126\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.448\u003csup\u003e**\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.453\u003csup\u003e**\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e-0.172\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e \u003cp\u003e-0.046\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGlucose\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-0.074\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.811\u003csup\u003e**\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-0.021\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-0.128\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.049\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e-0.038\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e-0.045\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e \u003cp\u003e0.529\u003csup\u003e**\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSucrose\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.476\u003csup\u003e**\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.025\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-0.145\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-0.138\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e-0.286\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e-0.111\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e \u003cp\u003e0.475\u003csup\u003e**\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal sugar\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-0.072\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-0.201\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.086\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e-0.055\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e-0.145\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e \u003cp\u003e0.630\u003csup\u003e**\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eQuininic acid\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1.000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.009\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-0.261\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e-0.173\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e-0.025\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e \u003cp\u003e0.077\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMalic acid\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1.000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e\u0026minus;\u0026thinsp;.598\u003csup\u003e**\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e-0.005\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e0.035\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e \u003cp\u003e-0.193\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCitric acid\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e1.000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.795\u003csup\u003e**\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e-0.289\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e \u003cp\u003e-0.457\u003csup\u003e**\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal acid\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e1.000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e-0.352\u003csup\u003e**\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e \u003cp\u003e-0.728\u003csup\u003e**\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMalic acid/\u003c/p\u003e \u003cp\u003ecitric acid\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e1.000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e \u003cp\u003e0.290\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSugars/acids\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e \u003cp\u003e1.000\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"11\" nameend=\"c11\" namest=\"c1\"\u003e \u003cp\u003eNote: Total of 64 apricot resources were considered and replicated measurements for each cultivars were averaged. Correlations were significant * at the 5% and ** 1%.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"1\" nameend=\"c12\" namest=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eDevelopment trends for sugar and organic acids in apricot fruits\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSince no extreme glu-type germplasm was identified in the apricot fruit resources, we screened the two-sugar-type and suc-type resources, thoroughly exploring the variability in sugar levels during fruit development. During the developmental cycle of the fruits of apricot resources, the glucose contents change very little. Among them, the glucose contents in the two-sugar-type apricot fruits approximately double during the ripening stage, while the change in the suc-type fruit is not significant.\u003c/p\u003e \u003cp\u003eBoth fructose and sucrose contents are maintained at relatively low levels during the early development and expansion stages. However, the two sugar levels increase differently when the fruit reaches maturity, about 7\u0026ndash;14 days before the fruit is fully ripe. Among them, in the two-sugar-type apricot varieties \u0026lsquo;Shunpingganzhi\u0026rsquo; and \u0026lsquo;Hamazui\u0026rsquo;, the increases in fructose and sucrose contents are similar, both 6\u0026ndash;9-fold. In contrast, the fructose contents of \u0026lsquo;Qingmisha\u0026rsquo; and \u0026lsquo;Lanzhoudajie\u0026rsquo; increase 2\u0026ndash;4-fold during the ripening stage, but their sucrose content increases\u0026thinsp;~\u0026thinsp;10-fold (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn the course of development, the quininic-acid contents change little, but then changes significantly with the maturity of the fruit. At the same time, malic acid, as the main organic acid in the apricot fruit, always maintains a high level during the fruit growth and development process. However, as the fruit enters the ripening stage (7\u0026ndash;14 days before maturity), the malic-acid contents all show significant downward trends.\u003c/p\u003e \u003cp\u003eThe malic-acid content is decreased to 30\u0026ndash;50% that of the developmental stage in the ripening stage and to 20% or even lower in the cit-type resources. Although the content of citric acid is low in the fruit growth and development stage, in middle and late fruit development, its content increases significantly in the cit-type and two-acid-type apricot fruits. Since a relatively high initial content of malic acid is observed, followed by a large decrease in the mature period, the total-organic-acid contents also show an overall decreasing trend (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eThe sugars in fruits mainly include fructose, glucose, and sucrose, so different varieties can be divided into reducing-sugar-type, suc-type, and two-sugar-type fruits based on their characteristics (Lijing et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). In this study, a systematic analysis of the sugar compositions of natural populations and fresh apricot fruits showed that the fructose content is lower compared with the other two sugars, and there are differences between varieties, which is consistent with previous reports (Baccichet et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). In cultivated apricot fruits, the glucose and sucrose contents and their ratios show remarkable diversity among different varieties. By setting∣log\u003csub\u003e2\u003c/sub\u003e (G/S)∣\u0026lt; 1.5 as a criterion, this study divides fruit into sucrose, glucose (reducing-sugar type), and two-sugar types. Among them, two-sugar resources account for more than 80%, sucrose resources account for about 15%, and the existence of extreme suc-type apricot varieties and glucose (reducing-sugar) resources is extremely rare. It is important to note that existing research focuses on different sugar contents in apricot fruit, and with the formula in this study, can also introduce similar sugar classification, for example, Caliskan et al. classified 15 apricot resource varieties into two sucrose, one glu-type (reducing sugar), and 12 two-sugar types (Supplementary Table\u0026nbsp;4) (Caliskan et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). In fact, this difference in sugar composition is very common in apricot fruits, and many studies have highlighted this point, but few studies have fully explored this phenomenon.\u003c/p\u003e \u003cp\u003eFrom the perspective of fruit development, the proportional distribution of sugar has stage characteristics. In the ripening stage, the type of sugar changes, while in the young and expansion stages, reducing sugars such as fructose and glucose are dominant, acting as the main energy materials for the development of reduced sugar crops (Li et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). When the apricot fruit enters maturity, organic matter accumulates mainly as sucrose, leading to a change in the sugar type of the fruit. The results of our correlation analysis indicate that fructose, glucose, and sucrose are negatively correlated, that is, the reduced-sugar content decreases and is converted into sucrose, which gradually accumulates in the fruit. This trend is also seen in fruits such as apples, citrus, and peaches (Du et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Jing et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Kongjie et al. 2022; Yanping et al. 2007).\u003c/p\u003e \u003cp\u003eAnother key factor affecting the taste of apricot is the organic acid content, the average value of which is 12.60 ± 0.48 mg/g FW, making it a high-acid fruit and thus unappetizing to certain consumer groups. In this study, an extremely high proportion of citric acid varieties were present in apricot fruits. Therefore, we classified the fruit acid type according to the log\u003csub\u003e2\u003c/sub\u003e (M/C) criteria presented above. Previous studies have pointed out that the organic acids in apricot fruits can be classified as malic acid and citric acid, but only two varieties, New (malic acid) and Kate (citric acid), have been studied, providing results that are consistent with those of this study (Meixia et al. 2006). In addition, when the apricot varieties reported in the literature were classified, we found that the log\u003csub\u003e2\u003c/sub\u003e (M/C) values of ‘Dajiexing’, ‘Kaili’ and ‘Luotuohuang’ were 4.00, 7.45, and 6.60, respectively, belonging to the mal-type, which are consistent with the classification results in this study (Fan et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Zhang et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). Similarly, log\u003csub\u003e2\u003c/sub\u003e (M/C) values of − 2.43 and − 2.06 have been reported for Kate, classifying it as cit-type, which is consistent with our study results (log\u003csub\u003e2\u003c/sub\u003e (M/C) = − 2.83) (Chen et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Fan et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). In fact, French researchers have long been aware of the diversity in malic acid and citric acid contents in apricot germplasm resources, and revealed the genotype differences in the ratio of malic acid/citric acid through principal component analys\u003cem\u003eis\u003c/em\u003e (Gurrieri et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2001\u003c/span\u003e). This finding coincides with the results of the present study.\u003c/p\u003e \u003cp\u003eHowever, apricot fruits are not rich in organic acid species. This study classified apricot resources into mal-type, cit-type, and two-acid type, and found that malic acid accounted for more than 90% of the total acid in the fruit development stage, while the other acids were less abundant, accounting for less than 10%. This rule is consistent with the organic acid changes in developing fruits such as apple and jujube, which are dominated by malic acid (Jing et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Zhang et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The richness of apricot fruit acid types is mainly reflected in the fruit ripening period. Although the total-acid content decreases, which is mainly due to the lower malic-acid content, the citric-acid content increases in some varieties.\u003c/p\u003e \u003cp\u003eThe results of correlation analyses for natural apricot group and resource fruit also confirmed that citric-acid content is negatively correlated with malic-acid content. Malic and citric acid, as intermediate metabolites in the tricarboxylic acid cycle, play important roles in plants, among which malic acid also participates in glycolysis and the glyoxylate cycle, as well as and other life activities (Huang et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). When the fruit is ripe, malic acid and citric acid are stored in vacuoles in plant cells by transport involving a wide variety of transport proteins, such as citric acid transporter proteins, the dicarboxylatetricarboxylate carrier, the vacuolar membrane dicarboxylic acid transporter protein, the tonoplast dicarboxylate transporter (TDT), and the proton pump protein. Studies have found that the main transporter of malic acid is the TDT, and overexpression of the transporter gene SlTDT, encoding the vacuole membrane in tomato, can increase the malic-acid content in fruit and reduce the citric-acid content, while the inhibition of the expression of this gene leads to decreased malic-acid content and increased citric-acid content (Liu et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Shi et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Zheng et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Therefore, this study speculates that the diversity of organic acid types in apricot resource fruits is not only related to the ripening stage of the fruit, but also to the type of transporter proteins activated by different varieties during the ripening stage.\u003c/p\u003e \u003cp\u003eSugar and organic acids in fruits are the main accumulation forms of carbon assimilates in plants, and they can be interconverted through various enzymatic reactions (Aprea et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Sweetman et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Wu et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). In this study, fructose was inversely correlated with citric-acid and total-acid contents in apricot fruit. Reducing sugars such as fructose and glucose are converted to fructose 6-phosphate and glucose 6-phosphate, catalyzed by phosphokinase, thus entering the tricarboxylic acid cycle to produce citric acid (Kongjie et al. 2022). Numerous studies have shown that the accumulation of organic acids in fruits is mainly determined by the energy released by organic acid transporters and ATP hydrolysis on the vacuole membrane (Gai et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Wang et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Yu et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). As key substances in the glycolytic pathway, fructose provides a crucial energy source for intracellular life activities.\u003c/p\u003e "},{"header":"Conclusions","content":"\u003cp\u003eThrough a deep analysis of the compositions of sugars and organic acids in apricot fruit, we have provided a solid theoretical basis for the improvement of apricot cultivation. In addition, our classification method based on sugar and organic acid characteristics not only facilitates the standardization of resources from various countries, it also promotes the effective utilization and development of apricot germplasm resources. In conclusion, this study provides important scientific data and practical guidance for the improvement of apricot fruit quality and breeding practice.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthor contribution statement\u0026nbsp;\u003c/strong\u003e \u003cstrong\u003eChenjuan\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eJing\u003c/strong\u003e and \u003cstrong\u003eXiaohong\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eWu\u003c/strong\u003e: study conception and design. \u003cstrong\u003eChenjuan Jing\u003c/strong\u003e,\u003cstrong\u003e\u0026nbsp;Duan Wang\u003c/strong\u003e, and \u003cstrong\u003eZhikun Liu\u003c/strong\u003e: data collection. \u003cstrong\u003eChenjuan Jing, Zhikun Liu\u003c/strong\u003e, and \u003cstrong\u003eXuefeng Chen\u003c/strong\u003e: analysis and interpretation of results, draft manuscript preparation. \u003cstrong\u003eChenjuan Jing\u003c/strong\u003e: Writing–review \u0026amp; editing. \u003cstrong\u003eChenjuan\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eJing\u003c/strong\u003e, \u003cstrong\u003eDuan Wang\u003c/strong\u003e, and \u003cstrong\u003eXiaohong\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eWu\u003c/strong\u003e: project administration and funding acquisition. All authors reviewed the results and approved the final version of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003eThis work was supported by Basic Research Funds of Hebei Academy of Agriculture and Forestry Sciences (No2024100202), HAAFS Science and Technology Innovation Special Project (2022KJCXZX-SGS-8), S\u0026amp;T Program of Hebei (21326310D) and Hebei Agriculture Research System (HBCT2024150210).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompliance with ethical standard\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest\u0026nbsp;\u003c/strong\u003eThe authors declare that they have no conflict of interest.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAprea E, Charles M, Endrizzi I, Laura C M, Betta E, Biasioli F Gasperi F (2017 ) Sweet taste in apple: the role of sorbitol, individual sugars, organic acids and volatile compounds. 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Acta Horticulturae Sinica 49: 2543\u0026ndash;2558\u003c/li\u003e\n\u003cli\u003eLi M, Li P, Ma F, Dandekar AM, Cheng L (2018) Sugar metabolism and accumulation in the fruit of transgenic apple trees with decreased sorbitol synthesis. Horticulture research 5: 60\u003c/li\u003e\n\u003cli\u003eLijing Z, Jiyun N, Zhen Y (2015) Advances in research on sugars，organic acids and their effects on taste of fruits. Journal of Fruit Science 32: 304-312\u003c/li\u003e\n\u003cli\u003eLiu R, Li B, Qin G, Zhang Z, Tian S (2017) Identification and functional characterization of a tonoplast dicarboxylate transporter in tomato (Solanum lycopersicum). Front Plant Sci 8: 186\u003c/li\u003e\n\u003cli\u003eLiu W, Liu N, Yu X, Zhang Y, Sun M, Xu M (2010) Apricot germplasm resources and their utilization in China, 862 ed. 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Scientia Agricultura Sinica 49: 3188-3198\u003c/li\u003e\n\u003cli\u003eSweetman C, Deluc LG, Cramer GR Ford, CM Soole KL (2009) Regulation of malate metabolism in grape berry and other developing fruits. Phytochemistry 70: 1329-1344\u003c/li\u003e\n\u003cli\u003eWang C, Xiang Y, Qian D (2021) Current progress in plant V-ATPase: from biochemical properties to physiological functions. J Plant Physiol\u003c/li\u003e\n\u003cli\u003eWang Y, Zhang J, Sun H, Ning N, Yang L (2011) Construction and evaluation of a primary core collection of apricot germplasm in China. Scientia Horticulturae 128: 311-319\u003c/li\u003e\n\u003cli\u003eWu S, Li M, Zhang C, Tan Q, Yang X, Sun X, Pan Z, Deng X, Hu C (2021) Effects of phosphorus on fruit soluble sugar and citric acid accumulations in citrus. Plant Physiol Biochem 160: 73-81\u003c/li\u003e\n\u003cli\u003eYan L, Jian N, Qing C (2007) Review on the factors to influence on the metabolism of sugars and acids in peach fruit. Chinese Agricultural Science Bulletin 23: 212-216\u003c/li\u003e\n\u003cli\u003eYu JQ, Gu KD, Sun CH, Zhang QY, Wang JH, Ma FF, You CX, Hu DG, Hao YJ (2021) The apple bHLH transcription factor MdbHLH3 functions in determining the fruit carbohydrates and malate. Plant Biotechnology Journal 19: 285-299\u003c/li\u003e\n\u003cli\u003eZhang C, Geng Y, Liu H, Wu M, Bi J, Wang Z, Dong X, Li X (2023) Low-acidity ALUMINUM-DEPENDENT MALATE TRANSPORTER4 genotype determines malate content in cultivated jujube. Plant Physiol 191: 414-427\u003c/li\u003e\n\u003cli\u003eZhang LL, Liu WS, Liu YC, Liu N, Zhang YP (2010) Measurement of sugars,organic acids in 5 apricot cultivars by high performance liquid chromatography. Journal of Fruit Science 27: 119-123\u003c/li\u003e\n\u003cli\u003eZheng B, Zhao L, Jiang X, Cherono S, Liu J, Ogutu C, Ntini C, Zhang X, Han Y (2021) Assessment of organic acid accumulation and its related genes in peach. Food Chem 334, 127567\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"acta-physiologiae-plantarum","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"acpp","sideBox":"Learn more about [Acta Physiologiae Plantarum](http://link.springer.com/journal/11738)","snPcode":"11738","submissionUrl":"https://www.editorialmanager.com/acpp/default2.aspx","title":"Acta Physiologiae Plantarum","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Apricot fruit, Sugars, Malic-acid-type and citric-acid-type, Distribution characteristics","lastPublishedDoi":"10.21203/rs.3.rs-6028777/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6028777/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study systematically analyzed the distribution characteristics and developmental patterns of sugars and organic acids in apricots, exploring the accumulation and metabolism of organic acids, thus providing important information for improving fruit quality. High-performance liquid chromatography was used to determine the sugar and organic-acid contents and distributions in mature apricot fruits from 332 common seedlings and 64 germplasm resources. The results showed that glucose and sucrose are the main sugars in apricots, and the fruits were classified as sucrose-type, or two-sugar-type based on the calculated value of log\u003csub\u003e2\u003c/sub\u003e (glucose/sucrose). Malic and citric acids are the main organic acids in apricots, and the fruits were classified as malic-acid-type, citric-acid-type, or two-acid-type based on the value of log\u003csub\u003e2\u003c/sub\u003e (malic acid/citric acid). Analysis of the developmental patterns of sugars and organic acids in selected fruits revealed high glucose contents during their developmental stages. Fructose and sucrose contents were low, but increased during the ripening stage, particularly those of sucrose. Malic acid was the main organic acid during the development stage, accounting for over 90% of the total-organic-acid content. As the fruit matured, the malic-acid content decreased, while that of citric acid increased. Correlation analysis revealed a significant positive correlation between fructose and citric-acid contents, both of which increased during fruit ripening. Therefore, changes in citric-acid levels may be related to ripening. Overall, this result offers valuable foundation for improving flavor quality of apricot fruit.\u003c/p\u003e","manuscriptTitle":"Distribution and developmental characteristics of sugars and organic acids in fresh apricots","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-02-21 09:03:45","doi":"10.21203/rs.3.rs-6028777/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2025-09-13T09:02:36+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-02-19T08:07:43+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-02-17T05:52:53+00:00","index":"","fulltext":""},{"type":"submitted","content":"Acta Physiologiae Plantarum","date":"2025-02-14T03:35:10+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"acta-physiologiae-plantarum","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"acpp","sideBox":"Learn more about [Acta Physiologiae Plantarum](http://link.springer.com/journal/11738)","snPcode":"11738","submissionUrl":"https://www.editorialmanager.com/acpp/default2.aspx","title":"Acta Physiologiae Plantarum","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"8bb5e590-beed-48d6-b6cb-70ad1ea37f17","owner":[],"postedDate":"February 21st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2025-02-21T09:03:45+00:00","versionOfRecord":[],"versionCreatedAt":"2025-02-21 09:03:45","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6028777","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6028777","identity":"rs-6028777","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}